(1) Field of the Invention
This invention relates to temperature control of a furnace and more particularly, to a method of controlling a temperature of a heating furnace used for slabs prior to a hot rolling mill when the slabs having different temperature elevation patterns are continuously carried into the furnace.
In a heating furnace, control of the furnace temperature is effected generally in such a manner that the slabs carried into the furnace attain a target temperature before they are withdrawn from the furnace. Among the temperature control methods, there is a method which determines a temperature elevation pattern to the slabs with respect to their positions inside the furnace, and which performs heating of the slabs in accordance with this temperature elevation pattern it is surmised that this temperature elevation pattern varies with the charging temperature of the slabs, the target withdrawing temperature, the target withdrawing temperature, the residence time of the slabs in the furnace and their materials (kind of steel). The initial temperature of the slabs, for example, varies markedly, as will be described next.
In a hot strip mill, semi-finished metal products (e.g., slabs or thick plates) are stored in a storage zone called a steel bay until it is necessary to roll them. Hence, the slab temperature is substantially equal to the ambient temperature.
From the viewpoint of conserving energy, however, it is not desirable to cool the semi-finished products down to the ambient temperature and to heat them again at the time of rolling. Recently, hot slabs produced from the continuous casting process or blooming mill are heated in the furnace. However, cold slabs (hereinafter called "cold materials") unavoidably mix with the hot slabs for rolling when the slabs are carried to the furnace after their surface correction or when the requested kinds of products are different from the kinds of slabs supplied from the continuous casting line.
The temperature elevation pattern to the target temperature for heating the hot materials is different from that for heating the cold materials.
The present invention relates to a method of controlling the furnace temperature of a furnace when the materials having different temperature elevation patterns such as the abovementioned hot and cold materials are continuously carried into the heating furnace.
(2) Description of the Prior Art
Most of the prior art does not mention the temperature control of slabs having different temperature elevation patterns such as the hot materials and the cold materials described above.
As the prior art relating to the temperature control of a furnace, mention can be made of U.S. Pat. No. 3,604,695 entitled "Method and Apparatus for Controlling a Slab Reheat Furnace". This prior art estimates the average temperature of the slabs distributed in plural furnace zones as a function of temperatures measured in the zones, heat characteristics and size of the slabs, positions of the slabs in the zones and so on, and carries out heating in order to minimize the deviation of the estimated temperature from the desired slab temperature patterns. The reference does not teach or suggest anything about the correction of the set temperature when the charged slab temperature varies greatly.